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Abstract
1. The comparative response of naked neck (Nana) broiler chickens and their normally feathered (nana) full sibs to varied dietary energy levels was assessed under natural ambient conditions in a subtropical climate in two separate trials, one in winter (19·0 to 26·0°C) and the other in summer (28·1 to 37·4°C).
2. The chickens were fed on diets with 10·9, 11·5 or 12·1 MJ ME/kg and with a constant protein content of 200 g/kg from 1 to 42 d of age.
3. Both genotypes showed similar body weight, food intake and food conversion efficiency at 42 d of age. Body weight and food conversion efficiency improved on the diet with the highest energy content.
4. Apparent retention (AR) of crude protein (CP) was higher in nana chickens than in their Nana sibs in the winter trial, while no differences were observed for AR of dry matter (DM), crude fibre (CF), ether extract (EE) or calcium. In the summer trial, no difference in nutrient retention was seen between the genotypes. Increasing dietary energy had a positive influence on AR of DM, CP and EE.
5. The relative weights of feathers and skin were lower in Nana chickens than in their normal counterparts. Ready-to-cook yields were greater at the high dietary energy content, while abdominal fat increased with increasing energy content. Nana chickens had more skin protein and less fat in breast muscle and skin than their normal sibs in the summer trial.
6. It was concluded that the Nana broiler chickens showed similar performance and did not differ in dietary energy requirements in comparison to their nana sibs under natural ambient conditions in a subtropical climate.